1. Field of the Invention
The present invention relates to ionizing radiation detection systems, and more specifically, to a system and method for combining spectral data from disparate ionizing radiation detectors to obtain a standard radiation analysis.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Use of ionizing radiation detectors is well known. For spectroscopic ionizing radiation detection and measurement, performance is limited by various traits of the detector. For example, the detector's efficiency is limited by its size and intrinsic efficiency while the size is limited by manufacturing restraints specific to the detector type. The detector type also dictates its energy resolution, a key characteristic determining the quality of acquired data. The cost for such detectors is typically proportional to the aforementioned size and resolution capabilities.
The efficiency of a spectroscopic ionizing radiation measurement system can be improved by adding more detectors to the system. Historically, this has been done using detectors of the same type, each with the same peak response function. Summing measured spectra of like detectors after matching energy calibrations allows analysis of the final summed spectrum using the common peak response function.
An example of an application in which multiple detectors are commonly used is a traffic portal. Homeland security employs the use of radiation detection traffic portals through which vehicular traffic must pass. These portals are designed to scan cars, trucks, and other vehicles for the presence of radioactive materials.
Current spectroscopic portal systems typically use either an array of 4″×4″×16″ NaI(Tl) detectors or large HPGe semiconductor detectors. The scintillator system operates at room temperature and is able to employ a much greater mass of active detector volume for better efficiency at lower cost than HPGe. However, HPGe energy resolution is about 20-30 times better than NaI(Tl). The excellent energy resolution of HPGe allows greater confidence in coping with source masking scenarios and avoidance of excessive false positive identifications. Still, the burden of cryogenic cooling requirements and higher cost of HPGe per unit volume limits the degree of deployment.
Because all detectors are limited as to size, multiple detectors must be used in such a portal to monitor a broad area. This plurality of detectors is configured in an array. The common means for obtaining a reading from a multiple detector array is to simply sum the outputs and analyze the final summed spectrum. However, this requires detectors with the same peak response functions and energy resolutions. For a given cost, this requires a choice between either higher efficiency or higher energy resolution.
This traditional approach does not support combining different types of detectors with very different peak response functions. Further, attempting to use such standard summing in a system having different types of detectors would result in a summed spectrum with a complex multi-modal peak response function that would preclude standard analysis. Accordingly, a need exists for an ionizing radiation detection system and method that allows use of multiple detectors of different types and having different capabilities. The present invention satisfies this need and others as explained and described in the following detailed description.